The invention relates to a process for braking a vehicle and a braking system for carrying out that process.
A process for braking a vehicle is described in DE 35 02 825 A1. A braking device, called a "braking system with regulated deceleration," which functions according to this process, is disclosed in FIG. 2 of this disclosure. In the disclosed braking process, a control unit transmits a brake actuation signal to at least one energy distributor which supplies energy to at least one wheel brake. The energy is supplied so long as a signal which indicates the actual deceleration of the vehicle differs from a signal indicating the required deceleration produced by the driver.
When travelling downhill, the vehicle is subject to a downhill force which accelerates the vehicle, i.e., decelerates it negatively, if it is not braked by other means. When actuating the aforementioned braking system with regulated deceleration, the driver of the vehicle can only produce a vehicle deceleration requirement signal, by means of a deceleration transmitter, for a vehicle deceleration that is other than 0. The control unit then transmits a brake actuation signal until the vehicle deceleration requirement signal equals the signal indicating actual vehicle deceleration transmitted from a deceleration sensing device. This means that a vehicle equipped with the known braking system with regulated deceleration cannot be braked to zero deceleration, i.e., to a constant speed, when travelling downhill.
An object of the present invention is to further develop a process for braking a vehicle in which the vehicle can be simply braked to a constant speed when travelling downhill.
A vehicle equipped with the known braking system also has the disadvantage that it cannot be braked without a jolt on downhill travel. This is because the vehicle is abruptly "yanked over" from accelerated travel to decelerated travel by even the slightest actuation of the braking system, i.e., by even a very small vehicle deceleration requirement signal. This disadvantage is eliminated by the present invention.
When travelling uphill without power and without braking, e.g., when the driver switches from pressing the accelerator pedal to braking, an uphill force slows down the vehicle, resulting in a corresponding signal of the deceleration sensing device indicating the actual vehicle deceleration. When the aforementioned known braking system with regulated deceleration is actuated, the control unit generates no brake actuation signal so long as the driver fails to produce a vehicle deceleration requirement signal for a vehicle deceleration which is greater than the existing vehicle deceleration. Rather, the braking system remains inactive during that time. Hence, the driver actuates the braking system "on idle" and during that time has the sensation that the braking system has failed. This disadvantage is also eliminated by the invention.
With the known braking system with regulated deceleration, the interactions between the driver and the vehicle, when the driver actuates the braking system with a particular actuation force or actuation displacement, are under certain circumstances different from those to which the driver is accustomed for a conventional vehicle equipped with a conventional braking system. Such interactions between the driver and the vehicle include bearing forces exerted by the driver upon the steering wheel, the driver seat, the safety belt, the floor of the driver's cabin, etc.
In a conventional braking system, which is energy, e.g., pressure, regulated, the driver transmits an energy requirement signal by applying a force or displacement to a transmitter. The transmitter in turn causes appropriate energy regulation devices to apply the appropriate amount of braking corresponding to that signal.
The driver of a vehicle equipped with a conventional braking system becomes accustomed to the correlation between the above-mentioned interactions and the resulting vehicle deceleration. When travelling uphill without power and without braking, the uphill deceleration force thus acts upon the vehicle and thereby upon the driver who is unaware of any interaction with the vehicle. Only the additional vehicle deceleration caused by an actuation of the braking system makes the driver feel interactions. To the driver, these interactions are no different from those occurring when the braking system is actuated on flat ground. Similarly, when the vehicle travels downhill without power and without braking, the accelerating downhill force acts upon the vehicle and the driver without producing any driver awareness of interaction with the vehicle. In this case too, the driver becomes accustomed to the "learned correlations" when actuating the brake. This lack of awareness to interactions also applies for braking when the downhill force exceeds the braking force so that vehicle and driver accelerate in spite of the actuation of the braking system.
In a vehicle equipped with the known braking system with regulated deceleration, the deceleration sensing device produces a signal indicating actual vehicle deceleration when travelling uphill without power and without braking. This actual vehicle deceleration signal corresponds to the vehicle deceleration caused by the uphill deceleration force. If the driver now actuates the braking system, the control unit therein causes only so much brake energy to be applied at the wheel brake as is required to cancel out the difference between the signal indicating actual vehicle deceleration (which is based on the uphill decelerating force) and the vehicle deceleration requirement signal. The driver senses only interactions based on this additional deceleration. Thus, the driver has the sensation that the braking system is failing when driving uphill. On the other hand, when actuating the braking system while travelling downhill without power or brake, the driver detects interactions which, in addition to those corresponding to the vehicle deceleration requirement signal, are based on the neutralization of the pre-braking accelerating downhill force. For this reason, the driver has the sensation when driving downhill that his braking system is very good.
Different interactions not only reduce the driver's comfort but also impede the driver's ability to develop a sensitivity to the dependency between actuating force or actuating displacement and the resulting vehicle deceleration. As a consequence, it is difficult for the driver to detect any possible defects in the braking system from its behavior.
Hence, a further object of the present invention is to eliminate the above-described disadvantages or differences in interactions occurring when the different braking systems are actuated. Any changes occurring with respect to the normal interactions experienced while actuating the braking system according to the invention, indicate a malfunction in the electrical components of the braking system.